Increasingly, individuals are reading electronic versions of books, also referred to in some cases as “eBooks” or “electronic books,” via their client devices, such as electronic reader devices, smart phones, tablet computers, and the like. Supplemental content associated with electronic books is also becoming more prevalent. For example, individuals may post comments about electronic books they are reading to social networking sites and/or micro-blogging sites. Further, individuals may provide annotations associated with electronic books as they are reading the electronic books. In some cases, the annotations may be collected by one or more service providers or publishers and made available to certain individuals reading an electronic book. In addition, information about electronic books and authors of electronic books may be available via a number of sites, such as media outlet sites, blogging sites, and so forth. However, it can be inefficient and time consuming to aggregate supplemental content associated with electronic books from a number of sources. Additionally, individuals may not even be aware of all of the supplemental content that is available for an electronic book. Further, client devices generally provide limited mechanisms for controlling the rendering of supplemental content while reading an electronic book.